Conventionally, a coaxial nozzle for a laser (a laser nozzle) 200 is inclined by 10° to 20° with respect to a machining surface of a work W, in order to prevent a reflected light from a welded portion from damaging a laser oscillator and its optical system by returning to a laser oscillator and its optical system, at a time of welding a work (see FIG. 2).
Note that the patent document 1 and the patent document 2 can be listed as the documents related to the prior art.